Transition Metals

What is a transition metal?

A d-block element that can form at least one stable ion with a partially filled d-subshell

Which two d-block elements are NOT transition metals?

Scandium (Sc) and Zinc (Zn)

What are the four key properties of transition metals?

Variable oxidation states, coloured ions in solution, good catalysts, and ability to form complexes

What is a ligand?

A molecule or ion that donates at least lone pair of electrons to form a dative covalent bond with a central metal ion

What is a complex ion?

A central metal ion bonded to one or more ligands by coordinate bonds

What is coordination number?

The number of coordinate bonds formed from ligands to the central metal ion NOT the number of ligands

What is the coordination number and shape of [Cu(H₂O)₆]²⁺?

6, octahedral

What is the coordination number and shape of [CuCl₄]²⁻?

4, tetrahedral

What is the coordination number and shape of [Ag(NH₃)₂]⁺?

2, linear

What is a monodentate ligand and list the 3 examples?

A ligand that can form one coordinate bond with a metal ion as it only have 1 lone pair (e.g. H₂O, NH₃, Cl⁻)

What is a bidentate ligand and list the 2 examples?

A ligand that can form two coordinate bonds with a metal ion as it has 2 lone pairs on separate atoms on the molecule (e.g. H₂NCH₂CH₂NH₂,(ethane-1.2-diamine) C₂O₄²⁻ (ethanedioate))

What is the chelate effect?

The ability of multidentate ligands to form more stable complexes than similar monodentate ligands

What is the colour of [Fe(H₂O)₆]²⁺?

Pale green solution

What is the colour of [Fe(H₂O)₆]³⁺?

Purple solution (often appears yellow/brown due to hydrolysis)

What is the formula and colour of [Cu(H₂O)₆]²⁺?

Blue solution

What is the formula and colour of [Cr(H₂O)₆]³⁺?

Green/purple solution

What is the formula and colour of [Al(H₂O)₆]³⁺?

Colourless solution (Al³⁺ is not a transition metal but is often studied alongside)

Why do transition metal complexes appear coloured?

Electrons absorb visible light and move from lower energy d-orbitals to slightly higher energy d-orbitals (d-d transitions) electrons go from ground state to excited state

What 3 factors affect the colour of a transition metal complex?

Oxidation state of the metal, type of ligand, and coordination number

What colour is [Cu(NH₃)₄(H₂O)₂]²⁺?

Deep blue solution

What colour is [CuCl₄]²⁻?

Yellow/green solution

What colour is [CoCl₄]²⁻?

Blue solution

What is the electron configuration of a chromium (Cr) atom?

1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d⁵

What is the electron configuration of a copper (Cu) atom?

1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d¹⁰

What is unusual about chromium's electron configuration?

The 4s orbital only has one electron to allow the 3d orbital to be half-filled (3d⁵) which is more stable

What is unusual about copper's electron configuration?

The 4s orbital only has one electron to allow the 3d orbital to be fully filled (3d¹⁰) which is more stable

Why do transition metals have variable oxidation states?

The 4s and 3d energy levels are very close, so electrons can be gained or lost using a similar amount of energy

What is the colour of VO₂⁺ (vanadium +5)?

Yellow

What is the colour of VO²⁺ (vanadium +4)?

Blue

What is the colour of V³⁺ (vanadium +3)?

Green

What is the colour of V²⁺ (vanadium +2)?

Purple/ violet

What is the colour of MnO₄⁻ (manganate(VII))?

Purple

What is the colour of Mn²⁺?

Pale pink/colourless

What is the colour of Cr₂O₇²⁻ (dichromate(VI))?

Orange

What is the colour of Cr³⁺?

Green

What is a redox titration?

A titration used to find the concentration of a species by reacting it with an oxidising or reducing agent

What is a self-indicating reaction?

A reaction where one of the reactants or products acts as its own indicator by changing colour

Write the half-equation for reduction of MnO₄⁻ in acidic conditions.

MnO₄⁻ + 8H⁺ + 5e⁻ → Mn²⁺ + 4H₂O

Write the half-equation for reduction of Cr₂O₇²⁻ in acidic conditions.

Cr₂O₇²⁻ + 14H⁺ + 6e⁻ → 2Cr³⁺ + 7H₂O

Write the half-equation for oxidation of Fe²⁺ to Fe³⁺.

Fe²⁺ → Fe³⁺ + e⁻

What is the catalyst in the Haber Process?

Iron (Fe)

What is the catalyst in the Contact Process?

Vanadium(V) oxide (V₂O₅)

What is a heterogeneous catalyst?

A catalyst that is in a different physical state from the reactants

What is a homogeneous catalyst?

A catalyst that is in the same physical state/ phase as the reactants

What is autocatalysis?

A reaction where one of the products acts as a catalyst for the reaction

Give an example of autocatalysis.

The reaction between MnO₄⁻ and C₂O₄²⁻ where Mn²⁺ produced acts as a catalyst

How does a heterogeneous catalyst work?

Reactants are adsorbed onto the catalyst surface, weakening bonds and bringing them close together or preventing repulsion etc

What is complete ligand substitution?

All water ligands are replaced by new ligands

What is incomplete ligand substitution?

Only some water ligands are replaced, often occurring when substituting ligands of a different size

Write the equation for substitution of H₂O by NH₃ in [Cu(H₂O)₆]²⁺.

[Cu(H₂O)₆]²⁺ + 4NH₃ → [Cu(NH₃)₄(H₂O)₂]²⁺ + 4H₂O

Write the equation for substitution of H₂O by Cl⁻ in [Cu(H₂O)₆]²⁺ with excess HCl.

[Cu(H₂O)₆]²⁺ + 4Cl⁻ → [CuCl₄]²⁻ + 6H₂O

Write the equation for substitution of H₂O by Cl⁻ in [Co(H₂O)₆]²⁺ with excess HCl.

[Co(H₂O)₆]²⁺ + 4Cl⁻ → [CoCl₄]²⁻ + 6H₂O

What colour change occurs when [Co(H₂O)₆]²⁺ reacts with excess HCl?

Pink to blue

What colour change occurs when [Cu(H₂O)₆]²⁺ reacts with excess NH₃?

Pale blue to deep blue

What colour change occurs when [Cu(H₂O)₆]²⁺ reacts with excess HCl?

Blue to yellow/green

What is the formula of the complex formed between Ag⁺ and excess NH₃?

[Ag(NH₃)₂]⁺ (linear, coordination number 2)

What are the products, reactants and conditions of the Haber Process?

N₂ + 3H₂ ⇌ 2NH₃; iron catalyst (Fe), temperature 400-450°C, pressure 200 atm

How does the iron catalyst work in the Haber Process?

Adsorbs N₂ and H₂ onto its surface, weakening bonds and bringing molecules close together to react

Outline the 3 stages of the Contact Process.

Stage 1: S + O₂ → SO₂; Stage 2: 2SO₂ + O₂ ⇌ 2SO₃; Stage 3: SO₃ + H₂O → H₂SO₄

Write the equation for the catalytic step of the Contact Process.

2SO₂ + O₂ ⇌ 2SO₃ (catalysed by V₂O₅)

Why are transition metals good catalysts?

Variable oxidation states allow them to adsorb reactants and form intermediate species

What is catalytic poisoning?

Impurities in reactants bind irreversibly to the catalyst surface, blocking active sites and reducing efficiency

Why is purification of reactants important in the Haber Process?

To prevent catalytic poisoning of the iron catalyst by impurities like sulfur compounds